To evaluate the incidence and severity of ventricular arrhythmias (VA) in a large group of patients who underwent corrective surgery for tetralogy of Fallot (TF) more than 4 years previously (mean age at surgery: 6 years 5 months), cardiac catheterization and cineangiography as well as 24 hour ambulatory Holter electrocardiography (HE) were performed in 45 patients. Fifteen (33%) of the 45 patients had VA of Lown grade 2 or greater. Patients with VA (group I) were found to be significantly older at surgery than patients without VA (group II) (p less than 0.05). There were no significant differences in the ratio of postoperative right and left ventricular systolic pressures (RVSP/LVSP), and also right ventricular ejection fraction (RVEF) between the 2 groups. As far as we know, none of our patients has suffered a sudden late death after repair of TF. Still, the overall incidence of VA was significantly high.